Hit ENTER after each Tag to add it to your post; Numbers in parentheses represent the Tag's usage.
On the bottom it says
"Tag your post with keywords below; numbers shown in parentheses represents popularity."
Then when you go to type multiple tags out it just puts them all together as one tag.
Then I learned through trial and error you need to hit "Enter" or "Tab" after each tag you type in.
Why not just change the text to:
"Tag your post with keywords below; after each keyword you type in - press the "ENTER" or "TAB" key"
Then I wouldn't of been confused.